Deoxidation alloy



United States Patent 3,215,525 DEOXIDATION ALLOY Aloise F. Sprankle, Cambridge, Ohio, assignor to Vanadium Corporation of America, New York, N.Y., a corporation of Delaware Filed Oct. 12, 1962, Ser. No. 230,237 1 Claim. (Cl. 75-123) This invention relates to a new deoxidation alloy to be used in the processing of steel. This alloy is of great micrographic cleanliness and will be applied for the final deoxidation of steel in the ladle. It is particularly suited to be used for steels that are designed for service under high stresses.

A great many deoxidation agents have been used for the treatment of steels both in the furnace and in the ladle. Such agents frequently consist of or contain substantial amounts of silicon, aluminum, calcium, and other metals that are capable of removing the oxygen contained in the melt and binding it in such manner as to render it harmless or to cause it to rise from the melt into the slag.

It is of great importance, particularly in the manufacture of high-quality steels, that the deoxidation products are substantially completely removed from the steel, or, to the extent that this is not possible, that these inclusions be in such a condition that they cannot cause any substantial stress concentrations during service nor present difiiculties during the processing of the steel.

It is a further object of the invention to produce a deoxidation trolly having a low hydrogen content.

For many years one of the most widely used final deoxidizers has been an agent generally designated as calcium-silicon or calcium-silicide, a composition containing about 30 to 35% Ca and 60 to 65% Si, the balance being iron. This product has been found to have unusually strong deoxidation power and when added in relatively small amounts of the steel in the ladle, it was found capable of binding substantially all the oxygen contained in the metal. Those inclusions that would not rise out of the melt were found to be present in the steel in an innocuous form, i.e., well rounded and well dispersed. In this form little trouble was experienced in rolling or otherwise working the steel, and in service, the shape and distribution of the inclusions did not lead to serious concentration of stresses around or adjacent to the inclusions, because of their rounded shape.

It was found, however, that the calcium-silicide employed in this manner was seriously contaminated with inclusions of its own and a relatively poor utilization of the calcium contained in the alloy has rendered its use rather uneconomic.

It is an object of this invention to produce an effective deoxidizer for the treatment of steel.

It is another object of this invention to produce an elfective deoxidizer to be used in the treatment of steel in the ladle.

It is another object of this invention to produce a deoxidizer that will be eflective both with respect'to the removal of oxygen from the steel and utilization of the active agents contained in the alloy.

It is an additional object of this invention to produce a deoxidizer that is itself of great micrographic cleanliness and thus does not introduce contaminants into the steel in the ladle.

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Another feature of considerable significance in the manufacture of such alloy steels is that they should contain the lowest possible hydrogen. If hydrogen levels exceed such minimum values then a phenomenon known as flaking may occur under certain manufacturing practices which gives rise to internal weakness in the steel. The hydrogen may be introduced into the steel during manufacture by a variety of factors. It is, however, important that any alloying agent or deoxidizer used during manufacture contain the lowest possible quantity or amount of hydrogen.

My deoxidation alloy consists essentially of about 10 to 16% calcium, about 49 to 64% silicon and from 0 to about 2% aluminum, the sum of the calcium and silicon not exceeding about 74%, the balance being iron and incidental impurities. It was surprising to discover that an alloy of great micrographic cleanliness, i.e., of a cleanliness that is substantially greater than that usually encountered in calcium-silicide, could be produced by maintaining the sum of the calcium and silicon at a value not exceeding about 74% of the weight of the alloy.

When my alloy was tested by deoxidizing a heat of steel in the ladle, it was found that my alloy, in spite of its substantially lower calcium content, was at least as effective in deoxidizing the steel as the higher calcium content calcium-silicide.

In evaluating these results, it has been found that the alloy of this invention, being substantially cleaner than calcium-silicide, contains all of its active elements in the metallic phase, whereas the calcium-silicide contains substantial portions of calcium and a considerable quantity of silicon as oxides. Thus, in the alloy of this invention, virtually all of the calcium is available to react with the steel, while the more massive amounts of calcium present in calcium-silicide are not so available. Consequently, the alloy of this invention has been found to have a substantially greater efliciency and to react very effectively with the oxygen in the steel.

A further surprising discovery was that the hydrogen content of my deoxidation alloy was substantially lower than that found in calcium-silicide. In calcium-silicide, the hydrogen generally amounts to 20-100 p.p.m.; whereas, in the deoxidation alloy according to this invention, it ranges between 4.4 and 9.6 p.p.m. As above pointed out, it is of considerable advantage in the manufacture of high quality steels to employ deoxidation alloys having as low a hydrogen content as possible.

The alloy of this invention was tested against the standard 30 to 35% Ca, 60 to Si calcium-silicide. Both alloys were added simultaneously to a heat of steel being tapped into two ladles through a bifurcated spout. My alloys used in these tests analyzed in one case 11.68% Ca, 62.48% Si, balance Fe and incidental impurities, in another 13.12% Ca, 60.40% Si, balance Fe and incidental impurities, While the calcium-silicide analyzed 32.18% Ca, 62.50% Si, balance Fe and incidential impurities.

These alloys were tested in the deoxidation of A181 52100 steel heats produced in a two-ton basic electric arc furnace, using double-slag practice. The heats were prepared from charges of pig iron, steel scrap, petroleum coke and lime. When melted down they contained 1.5% C and were then blown with oxygen. After removal of slag, 0.10% Si was added and aluminum was plunged into the bare bath. Heat A was treated with 1 /2 pounds per 3 ton of aluminum and heat B was treated with 1 pound. Before the second slag was prepared from lime, fluorspar and ferrosilicon, Cr was added as low carbon ferrochromium. Final additions of ferrosilicon and ferromanganese were made in the furnace 5 to minutes before tapping.

Heats A and B were tapped at 2800 and 2850 F. respectively, and each heat was halved by means of a bifurcated spout which fed one-half of each heat into each of two ladles, Nos. 1 and 2. In each case the calcium-silicide alloy was added to ladle No. 2, while one of my alloys was added to ladle No. 1. These alloys were introduced by means of plunging when the ladles were about two-thirds full.

The following table summarizes the ladle treatment:

and incidental impurities. FIGURE 2 is a photomicrograph of a portion of a sample of calcium-silicide which analyzed Ca 30.24%, Si 62.04%, balance Fe and incidental impurities. These two photomicrographs are 100x magnification and in the as polished condition. They illustrate the substantially greater inherent cleanliness of the alloy of this invention. This feature is of great significane especially in connection with a late-addition deoxidizing alloy which is intended to remove the last traces of oxygen from the heat of steel in such manner as to produce a minimum of inclusions and to leave any residues in the most favorable shape and random distribution in the resultant steel. Where such a final deoxidizer alloy itself contains substantial amounts of inclusions, it is obvious that it is not capable of performing its task as From heat A, two 1000 pound, 12 x 12 x chill cast ingots were produced, while from heat B two sand-cast ingots weighing 1500 pounds and measuring 13 x 13 x 36 were produced. In each case, the steel was teemed from the ladle into the mold through a 1" nozzle. A slow freezing rate was desired in the case of the sand-cast ingots so as to obtain larger inclusions than present in the bars rolled from the chill cast ingots. The sand-cast molds were made by ramming sand around an 18 gauge mild steel sheet forming the size of the desired ingot.

The steels produced came under the A151 standard desired and analyzed approximately as follows: 0.99% C., 0.41% Mn, .023% P, 035% S, 0.28% Si, 1.60% Cr.

Each of the chill cast ingots from heat A was hot pressed to 6 x 6" and then rolled to a 2" round bar. Each of the two 13 x 13 sand-cast ingots was forged to 5 x 5" and rolled to a 2" square bar.

For micrographic examination, longitudinal sections were taken from the bars representing top, middle, and bottom of the ingot. In addition, a slice was cut from the sand-cast ingots 4 from the shoulder, as well as samples representative of the edge and mid-section.

The micrographic examination of the chill cast ingot sections from Heat No. A showed inclusions that were well dispersed, fine and identified as largely duplex FeO and spinel and obtained from either deoxidation practice (ladle No. 1 or No.2).

The microexamination of samples from Heat No. B, representing the sand-cast ingots showed the same type of inclusions throughout, whether representing the edge or midsection of each as cast ingot. These inclusions were larger than those obtained by chill casting; they also tend to occur in clusters. Again there was little difference in appearance between the inclusions obtained by the method of this invention and that employing standard calciumsilicon.

Also, the examination of the longitudinal sections revealed no signficant difference. In all samples, from top, middle, and bottom of the ingots, individual inclusions appear to have approximately the same size and shape in the rolled condition as those observed in the ingot sample.

In order to illustrate the greater inherent microcleanliness of the alloy of this invention, reference is made to FIGURES 1 and 2. FIGURE 1 is a photomicrograph taken at random from a sample of the alloy of this invention analyzing Ca 14.28%, Si 58.05%, balance Fe advantageously as when it is clean in itself. It will be evident from the photomicrographs that the cleaner prodnet is much more capable of rapidly interacting with a metallic melt.

In order to illustrate the actual application of the alloy of thi invention, there is presented here below actual operational procedure and test results obtained on a commercial heat by a steel maker experienced in the production of high-quality, low-alloy steels.

In an SO-ton basic-lined electric steel furnace, a 70-ton heat of E4340 type steel was prepared. This analysis is of aircraft grade for service in high strength applications and thus should be of great cleanliness. Its manufacture must be carried out with great care and, as the following log will show, it includes the salient feature of this invention, namely, the use of a Ca-Si alloy containing 61% Si and 12% Ca for final deoxidation.

Time: Addition 2:45 Previous tap.

3:20 First charge12,400 lb.

mold; 41,100 lb. 4300 crops; 20,200 lb. Cr.-Ni-Mo; 20,700 lb. No. 1 bushelings.

7:10 Second charge-30,100 lb.

8600 turnings; 13,200 lb. N0. 1 bushelings; 4,000 lb. lime; 400 lb. nickel.

8:40 Bath analysis-0.48% C,

0.28% Mn, 0.021% S, 0.26% Cr, 0.79% Ni, 0.15% Mo, 0.13% Cu, 0.014% Sn.

9:05 200 lb. ore.

9:05-9:10 Removed slag.

9: 16 lb. Mo oxide.

9:25-9:28 Removed slag.

9:32 1100 lb. nickel.

9:43 Removed slag.

9:56 Ore added.

10:05 Bath analysis0.27% C,

10:10-10:12 Oxygen.

10:19 300 lb. FeMn; 1 spar.

10:20 Slag-off.

10:32 40 lb. Mo oxide; 260 lb.

nickel.

Time:Continued Addition :40-10:48 Slag-off.

10:50 250 lb. Ca-Si-Al.

10:52 1400 lb. lime; 450 lb. sand;

500 lb. spar; 300 lb. coke breeze.

11:10 Bath analysis0.26% C,

0.32% Mn, 0.017% S, 0.24% Cr, 1.60% Ni, 0.21% Mo.

11:15 lb. aluminum.

11:37 600 lb. FeSi.

11:42 400 lb. FeMn.

11:45 1100-1b. F GL 11:49 410 lb. FeMn.

12:07 lb. aluminum.

12:14 Start tap; 135 lb. coke.

12:17 250 lb. CaSi.

12:24 Finish tap.

1 FeMn contains 6% C, 78% Mn. 2 FeSi contains 50% Si.

3 FeCr contains 5% C, Cr.

4 Casi contains 61% S1, 12% Ca.

Final analysis: 0.39% C, 0.85% Mn, 0.011% P, 0.015% S, 0.35% Si, 0.90% Cr, 1.80% Ni, 0.26% Mo, 1.17% Cu, 0.032% A1.

Ingots were cast from this steel and rolled into rounds followed by magnaflux testing. The results obtained on the basis of the magnaflux tests were found to be excellent. The steel had been properly deoxidized and was entirely acceptable. Inclusions were found to be small-in size and rounded in shape and thus quite innocuous.

I claim:

A deoxidation alloy consisting essentially of about 10%16% calcium, about 49%64% silicon and from 0% to about 2% aluminum, the sum of the calcium and silicon not exceeding about 74%, the balance being iron and incidental impurities, said alloy being characterized by a clean structure and a low hydrogen content.

OTHER REFERENCES Archiv fur das Eisenhuttenwesen, vol. 13, pages 309 to 316, published in 1940.

DAVID L. RECK, Primary Examiner. 

